Niobium (Nb) Plasma Etching Process (RIE or ICP-RIE)
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Material Properties and Applications of Niobium
Niobium is well-known as a superconductive material. The material shows the highest superconducting transition temperature (9.3K [−264 °C]) among metal materials and used for superconductive device fabrication (e.g. QUBIT). Sandwiched structure of superconducting-insulator-superconducting material (SIS junction) is called as Josephson Junction, and Niobium is a popular material as superconductive layer material. Niobium Nitride (NbN) is another superconductive material with transition temperature of 16K (−257 °C) higher than Niobium. NbN-based device fabrication is more complicated, but the higher transition temperature is beneficial to superconductive device application.
As a compound of Niobium, Lithium Niobate (LiNbO3) is used for SAW (Surface Acoustic Wave) filter fabrication due to its piezoelectric properties. LiNbO3 crystal also sees application in optical waveguide and modulator with low optical loss.
Why Niobium etching is important?
Integration of multi layers is a promising approach to expand application of superconductive device with Josephson Junction. As superconducting digital circuits have more complicated structure with multi layers, precise etching process of Nb and NbN become more critical in device fabrication. For instance, etch selectivity of Nb against insulation material base layer is important. Run-to-run reproducibility is another important factor because impurities could be formed in Nb layer.
Niobium etching examples
Wafer-scale Niobium etching (ICP-RIE)
Ø8″ Niobium etching was conducted over SiO2 under-layer using ICP-RIE. Vertical Nb etching profile was achieved with minimum SiO2 under-layer etching.
Nb etch rate: 136 nm/min
Ø8″ etch uniformity: +/-3.5%
Niobium etching using Bosch Process
Samco DRIE systems enable deep silicon etching using the Bosch Process. The Bosch Process is normally used for silicon etching with high aspect ratios, but the process is applicable to Niobium etching case.
525 nm deep Niobium etching was conducted using PR mask. Niobium side etching was controlled to within 30 nm. Etching of SiO2 under-layer was also controlled, and selectivity of 34 was achieved between Niobium and SiO2 under-layer.
Niobium etching using non-Bosch Process
Samco DRIE systems allow not only standard Bosch Process but also non-Bosch Process for wider process window in silicon etching profile control. While the Bosch process is a technique which alternates between depositing a protective film on the sidewall using a C4F8 plasma and etching the bottom of the trench or hole with SF6, the Non-Bosch process is a technique of simultaneously depositing a protective layer on the sidewall and directionally etching the bottom of the feature with ions.
Nb/AlOx etching was conducted using non-Bosch Process. High selectivity of 214 was achieved between Niobium and AlOx.
What Samco offers for Nb etching?
Samco provides RIE system and ICP-RIE system for Nb and NbN etching application. Our systems enable Nb and NbN etching with high selectivity and reproducibility. Optional endpoint monitor is available for precise etch stop. In addition to Nb and NbN etching processes, we cover insulator material etching for superconductive device fabrication.
CRAVITY (Clean Room for Analog & digital superconductivity) at AIST, Japan possesses multiple Samco systems of RIE, ICP-RIE and TEOS CVD for superconductive device fabrication. These systems support state-of-the-art foundry services at the facility.
Open-load RIE System RIE-10NR
The RIE-10NR is a novel low-cost, high-performance, fully automatic reactive ion etching system which meets the most demanding process requirements for non-corrosive gas chemistry. A computerized touch screen provides a user-friendly interface for parameter control and storage. The system enables accurate sidewall profile control and high etch selectivity between materials. With its sleek, compact design, the RIE-10NR requires minimal cleanroom space.
– Processing up to ø220 mm (Ø3” x 5, Ø4” x 3, Ø8” x 1)
– Highly selective anisotropic etching meets demanding process requirements
– Fully automatic “one-button” operation with full manual override
– A computerized touch screen provides a user-friendly interface for parameter control and storage
– Automatic pressure control that allows for precise control of process pressure independent of gas flow
– Dry pump and system layout allow for ease of maintenance
– The reliable and durable system with a global installed base of more than 400 systems
Loadlock RIE System RIE-200NL
The RIE-200NL is a loadlock type reactive ion etching system that improves process repeatability and allows for corrosive gas chemistry. A fully optimized process chamber design provides excellent uniformity on ø8″ wafers or ø220 mm carrier trays of smaller wafers. The system enables accurate sidewall profile control and high etch selectivity between materials. With its sleek, compact design, the RIE-200NL requires minimal cleanroom space.
– Processing up to ø220 mm (ø3” x 5, ø4” x 3, ø8” x 1)
– A symmetrical evacuation design improves etching uniformity
– The process chamber is isolated from the environment by a loadlock chamber, which improves process repeatability and allows for corrosive gas chemistry
– A computerized touch screen provides a user-friendly interface for parameter control and storage
– Automatic pressure control that allows for precise control of process pressure independent of gas flow
– Dry pump and system layout allow for ease of maintenance
– With its sleek, compact design, the RIE-200NL requires minimal cleanroom space
ICP-RIE System RIE-400iP
The RIE-400iP is a load lock type etching system for high precision and high uniform processing of various semiconductor and insulating films. Inductively coupled plasma (Inductively Coupled Plasma), which uses a unique tornado coil, is used as the discharge form to produce a uniform, high-density plasma. In addition, you can select the appropriate plasma source according to the processing material and the processing content.
– ICP source “HSTC™ (Hyper Symmetrical Tornado Coil) delivers high RF power (2 kW or more) efficiently with good uniformity
– Exhaust system directly connected to the reaction chamber for a wide range of process windows from small flow and low pressure ranges to large flow and high pressure ranges
– Endpoint monitor (OES and/or Interferometric) for precise etch stop at the target film thickness
– Easy-to-maintain design
